CN108290819B

CN108290819B - Process for preparing diaryl carbonates

Info

Publication number: CN108290819B
Application number: CN201680069258.4A
Authority: CN
Inventors: 俞坤泉; G·G·瓦伯茨安
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2015-11-26
Filing date: 2016-11-24
Publication date: 2021-10-26
Anticipated expiration: 2036-11-24
Also published as: ES2761911T3; TW201720789A; EP3380450A1; TWI721044B; WO2017089441A1; CN108290819A; EP3380450B1; US20180354887A1; SG11201803481PA; US10315981B2

Abstract

A process for preparing diaryl carbonates from dialkyl carbonates and aryl alcohols is disclosed. The process is carried out in an apparatus comprising at least two distillation columns, and at least one of the distillation columns is operated at a pressure below atmospheric pressure achieved using a vacuum device.

Description

Process for preparing diaryl carbonates

Technical Field

The present invention relates to a process for the preparation of diaryl carbonates from dialkyl carbonates and aryl alcohols.

Background

Diaryl carbonates such as diphenyl carbonate can be prepared by a process in which a dialkyl carbonate such as diethyl carbonate or dimethyl carbonate is reacted with an aryl alcohol such as phenol. The process is typically carried out in two steps: a first step in which a dialkyl carbonate is reacted with an aryl alcohol in the presence of a transesterification catalyst to give an alkyl aryl carbonate; and a second step wherein the alkyl aryl carbonate undergoes disproportionation to yield diaryl carbonate and dialkyl carbonate. Examples of such processes are disclosed in US5344954, WO2011014374 and WO 2011067263.

The process is typically carried out in a series of distillation columns, some of which operate at subatmospheric pressure. The present inventors have observed that air can leak into a distillation column operating at a pressure below atmospheric pressure, which has several negative consequences. Oxygen and moisture from the air can cause side reactions to form undesirable trace impurities and color bodies. It can also react with the catalyst, deactivating it and precipitating out of the reaction solution in the case of homogeneous catalysts. The present inventors have sought to provide a method which avoids these problems.

Disclosure of Invention

Accordingly, the present invention provides:

a process for preparing a diaryl carbonate from a dialkyl carbonate and an aryl alcohol comprising:

a first step in which a dialkyl carbonate is reacted with an aryl alcohol in the presence of a transesterification catalyst to give an alkyl aryl carbonate and an alkyl alcohol; and

a second step in which the alkyl aryl carbonate undergoes disproportionation to give diaryl carbonate and dialkyl carbonate;

wherein the process is carried out in an apparatus comprising at least two distillation columns, and at least one of the distillation columns is operated at a sub-atmospheric pressure achieved using a vacuum device;

and wherein at least one distillation column operating at a pressure below atmospheric pressure has undergone a blow-by test, and the blow-by test shows no greater than 2 x 10^-3Air leakage rate of mbar.l/s.

The present inventors have found that by ensuring very limited oxygen access to the distillation column operating at subatmospheric pressure, it is possible to reduce the problems of side reactions and catalyst deactivation. Reducing the amount of side reactions should improve product quality and reduce the need for bleed-out of heavy components. Reducing catalyst deactivation should reduce the need for make-up catalyst. By following standard procedures for designing and implementing chemical processes, one skilled in the art will not adequately minimize oxygen ingress and will suffer from product quality and catalyst deactivation issues. The present inventors have recognized that the process for preparing diaryl carbonates can be improved by taking additional measures to reduce oxygen ingress.

Detailed Description

The present invention provides a process for the preparation of diaryl carbonate from dialkyl carbonate and aryl alcohol. The alkyl groups in the dialkyl and alkylaryl carbonates suitably have from 1 to 4, preferably from 1 to 3, carbon atoms. Preferably, the alkyl group is methyl or ethyl, more preferably ethyl. Preferably, the dialkyl carbonate is therefore dimethyl carbonate or diethyl carbonate, more preferably diethyl carbonate. The aryl group in the aryl alcohol, alkyl aryl carbonate and diaryl carbonate suitably has from 6 to 12 carbon atoms. Preferably, aryl is phenyl. Thus preferably, the aryl alcohol is phenol and the diaryl carbonate is diphenyl carbonate. Suitable examples of alkylaryl carbonates are methyl phenyl carbonate and ethyl phenyl carbonate.

In the first placeIn one step, a dialkyl carbonate is reacted with an aryl alcohol in the presence of a transesterification catalyst to obtain an alkyl aryl carbonate and an alkyl alcohol. The transesterification catalyst may be homogeneous or heterogeneous. Possible catalysts include the oxides, hydroxides, alcoholates, amides and hydrides of alkali metals and alkaline earth metals, for example sodium hydroxide or potassium hydroxide, or sodium methoxide or potassium methoxide or ethoxide or potassium ethoxide. Preferred catalysts comprise Lewis acid metal compounds, such as AlX₃、TiX₃、TiX₄、VX₅、ZnX₂、FeX₃And SnX₄And the like, wherein X is selected from the group consisting of: hydrogen, acetoxy, alkoxy, arylalkoxy and aryloxy. A particularly preferred catalyst is of the formula TiX₄Wherein X may be the same or different and is selected from alkoxy groups containing 1 to 6 carbon atoms, more preferably ethoxy or phenoxy groups.

Suitably, the concentration of catalyst is from 0.001 wt% to 2 wt% based on the total weight of the reactants comprising the catalyst. Preferably, the concentration is from 0.005 wt% to 1 wt%, more preferably from 0.01 wt% to 0.5 wt%.

In the second step, the alkyl aryl carbonate undergoes disproportionation to give diaryl carbonate and dialkyl carbonate. No additional catalyst is required for the disproportionation.

The process is carried out in an apparatus comprising at least two distillation columns. The distillation column is a typical column as used in chemical processes. Suitably, the apparatus comprises at least three distillation columns. Preferably, the apparatus comprises at least four distillation columns. Suitably, the apparatus may be as described in WO 2011067263. In a preferred embodiment of the invention, the apparatus comprises at least two and preferably three reactive distillation columns. A "reactive distillation column" is a distillation column containing a catalyst for effecting a chemical reaction in the distillation column. The reactive distillation column is preferably followed by another distillation column or columns which do not contain an effective amount of catalyst and which act as separation columns to separate the product, transesterification catalyst and by-products.

The pressure in the at least two distillation columns may vary within wide limits. At least one of the distillation columns is operated at a sub-atmospheric pressure achieved using a vacuum device. In a preferred embodiment, in which three reactive distillation columns are used, the pressure at the top of the first distillation column may be from 2 to 7bar, preferably from 2.5 to 5 bar. The pressure at the top of the second distillation column may be from 0.1bar to 3bar, preferably from 0.3bar to 1.5 bar. The pressure at the top of the third distillation column may be from 10mbar to 600mbar, preferably from 20mbar to 500 mbar. Preferably, the pressure at the top of the first distillation column is higher than the pressure at the top of the second distillation column, which in turn is higher than the pressure at the top of the third distillation column. In another preferred embodiment, wherein two reactive distillation columns are used, the pressure at the top of the first distillation column may be from 1.1bar to 7bar, preferably from 2bar to 5 bar. The pressure at the top of the second distillation column may be from 0.01bar to 1bar, preferably from 0.01bar to 0.6 bar.

The temperature in the distillation column or columns may also vary within wide limits. The temperature at the bottom of the one or more distillation columns may be from 50 ℃ to 350 ℃, preferably from 120 ℃ to 280 ℃, more preferably from 150 ℃ to 250 ℃, most preferably from 160 ℃ to 240 ℃.

In addition to the distillation column, the apparatus includes suitable piping and connections to connect the distillation column appropriately. The apparatus includes a vacuum device to create a sub-atmospheric pressure in the at least one distillation column. Suitable vacuum devices are well known to those skilled in the art. The apparatus suitably further comprises suitable heating and cooling means to achieve the preferred temperature in the distillation column.

The apparatus suitably comprises at least one recirculation loop whereby the reactant stream may be returned from one distillation column to an upstream distillation column. Preferably, there is a recirculation loop enabling the transesterification catalyst to be recirculated from the downstream reactive distillation column to the more upstream reactive distillation column.

At least one distillation column operating at a pressure below atmospheric pressure has been subjected to a leak test. A suitable leak test has the following steps:

(a) the distillation column is evacuated to vacuum at 500mbar (e.g. 60mbar)

(b) Separating the vacuum pump from the container and completely sealing the container

(c) Measuring the pressure increase in the container and determining the corresponding time

The pressure increase in mbar is divided by the time in minutes, giving a vacuum loss in mbar/min. Using this value and the volume of the distillation column, the air leakage rate in kg/h can be calculated using the following formula:

wherein M is_AFor air leakage in kg/h,. DELTA.p is the pressure change in mbar, t is the corresponding time in minutes and V is m³The equipment volume of the meter. The air leakage rate can be converted to an air leakage rate in mbar.l/s using the following conversion:

0.0043kg/h air at 20 ℃ under 1mbar.L/s

Air leakage test shows that the air leakage rate is not more than 2 x 10^-3mbar.L/s. Preferably, the air leak test shows an air leak rate of not more than 2 x 10^-4mbar.L/s. More preferably, the air leak test shows an air leak rate of not more than 2 x 10^- ⁵mbar.L/s. Most preferably, the air leak test shows an air leak rate of no greater than 1.2 x 10^-5mbar.L/s. It is desirable to enable a minimum air leak rate as this will reduce side reactions and catalyst deactivation problems. However, practical considerations will mean that there is a balance between minimizing the rate of air leakage and having an economical and efficient apparatus.

In an apparatus having multiple distillation columns operating at subatmospheric pressure, it is desirable that all of these distillation columns have undergone a leak test and all exhibit no more than 2 x 10^-3Air leakage rate of mbar.l/s. It is possible that one or more columns (especially those columns that are not reactive distillation columns) may have higher air leak rates, but this is not preferred.

By following standard procedures for designing and implementing the methods for preparing diaryl carbonates, one skilled in the art will not be able to followTo achieve not more than 2 x 10^-3Air leakage rate of mbar.l/s. For example, the following guidelines are given on the website of electric heating Systems, Inc (Thermo Systems Inc): for a typical chemical process vacuum system, based on a volume in the range of 1mm HgA to 50mm HgA under vacuum, the air leakage rate for this design (based on experience with multiple successful applications, in general) will be equal to the following amount:

volume under vacuum (ft)³)	Air leakage Rate (lb/hr)
		100	5
500	10
		700	15
1000	20
		1500	25
3000	50

This can be converted to m as follows³And air leakage rate in mbar:

as can be seen from the table, the air leakage rate obtained by following these guidelines is greater than the air leakage rate allowed in the method of the invention.

The present inventors have found that by minimising oxygen entering the apparatus (and in particular entering a distillation column operating at a sub-atmospheric pressure), it is possible to reduce the problems of side reactions and catalyst deactivation. Those skilled in the art must take various measures to ensure that the leak test shows no more than 2 x 10^-3Air leakage rate of mbar.l/s. One measure is to use the equipment and procedures normally used in high vacuum systems. For example, the stem and flange may all be fastened. Specially designed flange connections, for example with grooves and tongues or finely machined sealing surfaces and/or special seals, can be used. Instead of having a flanged connection, it may be desirable to have a welding unit in which different pieces of equipment are welded together, thus reducing the likelihood of air ingress. Another measure is to use an apparatus in which a purge gas (e.g., nitrogen) can be applied at a connection of the distillation column having a line that provides gas to and removes gas from the distillation column. Such devices are disclosed for example in US 2015136238. Flange elements may be connected to the pipeline, and one or more distillation columns and internal and external gaskets may be positioned between the flanges. A purge gas may be applied between the inner and outer seals to help prevent air from entering the connection between the line and the distillation column.

The present invention further provides a method for preparing polycarbonate by preparing a diaryl carbonate according to the method of the present invention and reacting the diaryl carbonate with a dihydroxy aromatic compound. Preferably, the dihydroxy aromatic compound is bisphenol A, which is 4,4' - (propan-2-ylidene) diphenol. Methods for preparing polycarbonates are disclosed in, for example, US5747609, WO2005026235 and WO 2009010486.

The invention is further illustrated by means of the following experiments.

Process for preparing diphenyl carbonateThermal degradation of

Experiments were conducted to show that air ingress affects the thermal degradation of diphenyl carbonate. A series of 50g samples of the same mass of diphenyl carbonate were heated in 100ml stainless steel closed containers under nitrogen and under air, respectively, to the temperatures shown in table 1 for a period of 3 hours. The APHA Pt-Co color number (which is a yellowness rating defined by ASTM D1209) of the DPC samples was measured after heating:

TABLE 1

Higher color numbers (increased yellowness) indicate degradation of diphenyl carbonate and formation of color bodies. This shows that air ingress, especially at elevated temperatures (in the above example at an oxygen content of about 200 ppm) can cause degradation of diphenyl carbonate. If the air leak rate is not controlled and the process for the production of diphenyl carbonate is designed according to standard principles, an oxygen content of 200ppm can easily be present in the distillation column, thus causing product degradation.

Claims

1. A method for preparing a diaryl carbonate from a dialkyl carbonate and an aryl alcohol, wherein the alkyl group in the dialkyl carbonate has 1 to 4 carbon atoms and the aryl group in the aryl alcohol has 6 to 12 carbon atoms, the method comprising:

a first step wherein the dialkyl carbonate is reacted with the aryl alcohol in the presence of a transesterification catalyst to yield an alkyl aryl carbonate and an alkyl alcohol; and

a second step wherein the alkyl aryl carbonate undergoes disproportionation to give diaryl carbonate and dialkyl carbonate;

and wherein the at least one vapor operated at a pressure below atmospheric pressureThe distillation column has undergone a gas leak test, and the gas leak test shows no greater than 2 x 10^-3Air leakage rate of mbar.l/s.

2. The process of claim 1, wherein the dialkyl carbonate is dimethyl carbonate or diethyl carbonate.

3. The method of claim 1 or claim 2, wherein the aryl alcohol is phenol and the diaryl carbonate is diphenyl carbonate.

4. The process of claim 1 or 2, wherein the transesterification catalyst is of the formula TiX₄Wherein X may be the same or different and is selected from alkoxy groups containing 1 to 6 carbon atoms.

5. The process according to claim 1 or 2, wherein the apparatus comprises at least two reactive distillation columns.

6. The method of claim 5, wherein the apparatus comprises three reactive distillation columns.

7. The process of claim 6, wherein the pressure at the top of a first reactive distillation column is 2 to 7bar, the pressure at the top of a second reactive distillation column is 0.1 to 3bar, and the pressure at the top of a third reactive distillation column is 10 to 600mbar, and the pressure at the top of the first reactive distillation column is higher than the pressure at the top of the second reactive distillation column, which in turn is higher than the pressure at the top of the third reactive distillation column.

8. The method of claim 1 or 2, wherein there is a connection between at least one distillation column operating at a pressure below atmospheric pressure and a line providing gas to or removing gas from the distillation column, and a purge gas is applied at the connection.

9. A method for preparing a polycarbonate by preparing a diaryl carbonate using the method of any one of claims 1-8 and reacting the diaryl carbonate with a dihydroxy aromatic compound.

10. The method of claim 9, wherein the dihydroxy aromatic compound is bisphenol a.